boost/type_erasure/same_type.hpp

0001 // Boost.TypeErasure library
0002 //
0003 // Copyright 2011 Steven Watanabe
0004 //
0005 // Distributed under the Boost Software License Version 1.0. (See
0006 // accompanying file LICENSE_1_0.txt or copy at
0007 // http://www.boost.org/LICENSE_1_0.txt)
0008 //
0009 // $Id$
0010
0011 #ifndef BOOST_TYPE_ERASURE_SAME_TYPE_HPP_INCLUDED
0012 #define BOOST_TYPE_ERASURE_SAME_TYPE_HPP_INCLUDED
0013
0014 namespace boost {
0015 namespace type_erasure {
0016
0017 /**
0018  * A built in concept that indicates that two
0019  * types are the same.  Either T or U or both
0020  * can be placeholders.
0021  *
0022  * \warning Any number of instances of @ref deduced
0023  * can be connected with @ref same_type, but there
0024  * should be at most one regular placeholder in
0025  * the group. same_type<_a, _b> is not allowed.
0026  * The reason for this is that the library needs
0027  * to normalize all the placeholders, and in this
0028  * context there is no way to decide whether to
0029  * use @ref _a or @ref _b.
0030  */
0031 template<class T, class U>
0032 struct same_type {};
0033
0034 }
0035 }
0036
0037 #endif